Semiconductor epitaxy bordering isolation structure

Abstract

A method includes providing a semiconductor structure having an active region and an isolation structure adjacent to the active region, the active region having source and drain regions sandwiching a channel region for a transistor, the semiconductor structure further having a gate structure over the channel region. The method further includes etching a trench in one of the source and drain regions, wherein the trench exposes a portion of a sidewall of the isolation structure, epitaxially growing a first semiconductor layer in the trench, epitaxially growing a second semiconductor layer over the first semiconductor layer, changing a crystalline facet orientation of a portion of a top surface of the second semiconductor layer by an etching process, and epitaxially growing a third semiconductor layer over the second semiconductor layer after the changing of the crystalline facet orientation.

What is claimed is: 
     
       1. A device comprising:
 a first gate structure disposed over a substrate; 
 an isolation structure at least partially embedded in the substrate; 
 a first semiconductor layer disposed on the semiconductor substrate and extending from the first gate structure toward the isolation structure; 
 a second semiconductor layer disposed directly on the first semiconductor layer, the second semiconductor layer extending from the first gate structure to the isolation structure; and 
 a third semiconductor layer disposed directly on the second semiconductor layer, the third semiconductor layer extending from the first gate structure to the isolation structure; and 
 an inter-layer dielectric (ILD) layer disposed over the isolation structure and the first gate structure, wherein the ILD layer is in direct contact with a sidewall of the isolation structure. 
 
     
     
       2. The device of  claim 1 , wherein the first semiconductor layer has a top slanted surface extending along a same plane from the first gate structure to the isolation structure,
 wherein the second semiconductor layer has a top surface that includes a first portion with a crystalline orientation of (1, 1, 1) and a second portion that is oriented in one of crystalline planes of {3, 1, 1}, {5, 1, 1}, {7, 1, 1}, and {9, 1, 1}, and 
 wherein the third semiconductor layer has a top surface that includes a first portion with a crystalline orientation of (1, 1, 1) and a second portion with a crystalline orientation of (0, 0, 1). 
 
     
     
       3. The device of  claim 1 , wherein the first gate structure includes a sidewall spacer, and
 wherein the first, second and third semiconductor layers physically contact the sidewall spacer. 
 
     
     
       4. The device of  claim 1 , wherein the first, second and third semiconductor layers form a source/drain feature associated with the first gate structure. 
     
     
       5. The device of  claim 1 , further comprising a second gate structure disposed directly on a top surface of the isolation structure. 
     
     
       6. The device of  claim 1 , wherein the first semiconductor layer includes a first dopant at a first concentration,
 wherein the second semiconductor layer includes the first dopant at a second concentration that is less than first concentration, and 
 wherein the third semiconductor layer includes the first dopant at a third concentration that is greater than first concentration. 
 
     
     
       7. The device of  claim 6 , wherein the first semiconductor layer is formed of a different material than the second semiconductor layer, and
 wherein the first semiconductor layer includes SiGe and the second semiconductor layer includes Si. 
 
     
     
       8. The device of  claim 6 , wherein the dopant is selected from the group consisting of boron and phosphorous. 
     
     
       9. A device comprising:
 a first gate structure disposed on a substrate; 
 a dielectric isolation structure disposed within the substrate; and 
 a first source/drain feature disposed in the substrate and associated with the first gate structure, wherein the first source/drain feature includes:
 a first semiconductor layer having a top slanted surface extending from the first gate to a sidewall of the dielectric isolation structure such that the first semiconductor layer is in direct contact with the sidewall of the dielectric isolation structure; 
 a second semiconductor layer disposed directly on the first semiconductor layer; and 
 a third semiconductor layer disposed directly on the second semiconductor layer; and 
 
 an inter-layer dielectric (ILD) layer disposed over the dielectric isolation structure and the first gate structure, wherein the ILD layer is in direct contact with the sidewall of the dielectric isolation structure. 
 
     
     
       10. The device of  claim 9 , wherein the first semiconductor layer includes a dopant at a first concentration and the third semiconductor layer includes the dopant at a second concentration that is greater than the first concentration. 
     
     
       11. The device of  claim 9 , wherein the first gate structure includes a high-k dielectric layer and a metal gate electrode disposed over the high-k dielectric layer. 
     
     
       12. The device of  claim 9 , wherein the second semiconductor layer and the third semiconductor layer interface with the dielectric isolation structure. 
     
     
       13. The device of  claim 9 , wherein only the first semiconductor layer of the first source/drain feature extends under the first gate structure. 
     
     
       14. A device comprising:
 a dielectric isolation feature disposed within the substrate; 
 a first gate structure disposed on the substrate; 
 a first source/drain feature disposed within the substrate on a first side of the first gate structure, the first side being opposite a second side of the first gate structure, wherein the first source/drain feature includes:
 a first semiconductor layer disposed within the substrate such that the first semiconductor layer extends below a topmost surface of the substrate; 
 a second semiconductor layer disposed on the first semiconductor layer and extending within the substrate below the topmost surface of the substrate; and 
 a third semiconductor layer disposed on the second semiconductor layer and extending within the substrate below the topmost surface of the substrate; and 
 
 a second source/drain feature disposed within the substrate on the second side of the first gate structure, wherein the second source/drain feature includes:
 a fourth semiconductor layer disposed within the substrate such that the fourth semiconductor layer extends below the topmost surface of the substrate; 
 a fifth semiconductor layer disposed on the fourth semiconductor layer, wherein no portion of the fifth semiconductor layer extends within the substrate below the topmost surface of the substrate; and 
 a sixth semiconductor layer disposed on the fifth semiconductor layer, wherein no portion of the sixth semiconductor layer extends within the substrate below the topmost surface of the substrate. 
 
 
     
     
       15. The device of  claim 14 , further comprising an interlayer dielectric layer disposed on the first gate structure and extending to a sidewall of the dielectric isolation feature. 
     
     
       16. The device of  claim 14 , wherein the first semiconductor layer is formed of a different material than the second semiconductor layer, and
 wherein the fourth semiconductor layer is formed of a different material than the fifth semiconductor layer. 
 
     
     
       17. The device of  claim 16 , wherein the first semiconductor layer and the fourth semiconductor layer include SiGe, and
 wherein the second semiconductor layer and the fifth semiconductor layer include Si. 
 
     
     
       18. The device of  claim 14 , wherein the first semiconductor layer is formed of the same material as the fourth semiconductor material, and
 wherein the second semiconductor layer is formed of the same material as the fifth semiconductor material, and 
 wherein the third semiconductor layer is formed of the same material as the sixth semiconductor material. 
 
     
     
       19. The device of  claim 18 , wherein a top surface of the first semiconductor layer has a first crystalline orientation and a top surface of the fourth semiconductor layer has a second crystalline orientation that is different than first crystalline orientation,
 wherein a top surface of the second semiconductor layer has a third crystalline orientation and a top surface of the fifth semiconductor layer has a fourth crystalline orientation that is different than third crystalline orientation, and 
 wherein a top surface of the third semiconductor layer has a fifth crystalline orientation and a top surface of the sixth semiconductor layer has a sixth crystalline orientation that is different than fifth crystalline orientation. 
 
     
     
       20. The device of  claim 19 , wherein the second, fourth and sixth crystalline orientations are the same.